Dustproof structure of communication device, using air filter having distributed dust collecting efficiency and pressure loss

ABSTRACT

A dustproof structure for a communication device is disclosed, in which the whole area of the air filter can be effectively used, the dust collecting efficiency can be improved at low cost, and an increase in the pressure loss can be prevented. The air filter comprises a first air filter section and a second air filter section, wherein the first air filter section is provided at an area closer to the fan, within which the air flow is concentrated, and the second air filter section is provided at another area farther from the fan, and the first air filter section has a dust collecting efficiency higher than that of the second air filter section, while the second air filter section has a pressure loss lower than that of the first air filter section.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a division of application Ser. No. 09/473,016, filedDec. 28, 1999 now U.S. Pat. No. 6,310,770, now pending, and related totwo concurrently filed applications, both entitled: Dustproof Structureof Communication Device, Using Air Filter Having Distributed DustCollecting Efficiency and Pressure Loss, and based on Japanese PatentApplication No. 10-374602, filed Dec. 28, 1998, by Masayuki Negishi.This application claims only subject matter disclosed in the parentapplication and therefore presents no new matter.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dustproof structure for acommunication device which has both an air cooling function and adustproof function using an air filter, and in particular, to adustproof structure employing an economical air filter arrangementhaving a high efficiency.

This application is based on Patent Application No. Hei 10-374602 filedin Japan, the contents of which are incorporated herein by reference.

2. Description of the Related Art

When a generally-known communication device having a shelf whichcontains a plurality of printed circuit boards is operated, electroniccomponents, electronic circuits, a power supply, and the like generateheat, and relevant thermal stress degrades the reliability of thedevice. Therefore, it is necessary to cool the heated portions anddischarge heat to the outside. Two kinds of cooling methods are known:natural air cooling and forced air cooling. In a modern communicationdevice having a high thermal density, the forced air cooling using a fanis commonly used.

There are two types of forced air cooling using a fan. One is thedraw-in method in which the fan is arranged at the exhaust side so thatthe air inside the chassis is drawn in and then expelled (or vented orexhausted) outside, and the other is the forcing method in which the fanis arranged at the suction side so that the outside air is forciblyintroduced into the chassis.

If dust comes into the communication device, it may lead an undesirableeffect such as contact failure, insulation failure, promotion ofcorrosion, degradation of the cooling effect, or the like. Therefore, ifthe communication device is used in a dusty area, a dustproof structureis necessary. For example, an air filter for filtering cooled air may beprovided at the suction side. Japanese Unexamined Patent Application,First Publication, No. Sho 60-183623, discloses an example of thedraw-in cooling method and a dustproof structure using an air filter.

Below, the above two forced air cooling methods will be compared inconsideration of the dustproof effect. In the draw-in method, an airfilter is provided at the air inlet, thereby preventing dust fromflowing from the inlet into the chassis; however, air that does not passthrough the air filter will flow through a gap or the like into thechassis together with dust. In the forcing method, an air filter isprovided at the air inlet and all the air forced into the chassis passesthrough the air filter; thus, if the performance of the air filter isexcellent, the reduction of dust introduced into the chassis can bemaximized. Therefore, the forcing method is much more effective than thesuction method in consideration of the dustproof effect.

Next, the air filter will be examined. Dust particles included in an airflow collide with and adhere to an air filter, and thereby the dust isremoved. A fibrous material, nonwoven fabric, porous plastics, wiregauze, sintered metal, or the like can be used for manufacturing the airfilter. The dust collecting efficiency and pressure loss are practicalindices indicating the performance of the air filter. Generally, thehigher the dust collecting efficiency, the greater the pressure loss is.An air filter having a higher dust collecting efficiency is effectivefor reducing the introduced dust. However, in this case, the pressureloss is also increased, which imposes a great burden on the air blowingsystem of the device.

Below, the air flow generated by the fan will be examined. In mostcases, the wind blown from the fan does not have a uniform velocitydistribution. For example, in the vicinity of the rotational shaft ofthe axial fan, an area having an extremely small wind velocity ispresent. Also in the axial fan, the spread of the ventilated area in theradial direction with respect to the rotational shaft is not very large,and the closer the area is to the fan, the more significant thistendency is. That is, in the vicinity of the fan, the spread of theventilated area is hardly observed, and thus the cross-sectional area ofthe air flow is approximately equal to the projected area of the fan.

Accordingly, as for the forced air cooling method in consideration ofthe dustproof effect, the forcing method is much more effective.However, in the forcing method, the air filter is provided immediatelybelow the fan, that is, positioned close to the fan. Such an arrangementmakes the air flow concentrate at a part of the air filter.

In order to improve the dust collecting efficiency, it is important toeffectively use the whole face or area of the air filter, and also toreduce the pressure loss as much as possible. A high-performance airfilter having a high dust-collecting efficiency and relatively smallpressure loss may be used; however, such a high-performance air filteris expensive and thus has a low economical efficiency.

Accordingly, a developed air-filter structure is required, whose wholearea can be effectively used, and which has a higher dust collectingefficiency and a lower pressure loss at low cost.

FIGS. 7 and 8 show an example structure, in which cabinet 22 havingprinted circuit boards installed is cooled by using the forced aircooling method. A fan shelf 23 is provided below the cabinet 22, and fanunit 25 is mounted in the fan shelf. One or more fans 24 are provided inthe fan unit 25. Each fan 24 is the axial type, and the blowingdirection is the wind direction. That is, the outside air is forciblyintroduced into the cabinet 22 by using the fans 24 in the forced aircooling method.

The cabinet 22 is not always used in a single structure, but a pluralityof cabinets 22 may be stacked one on the other. In such an arrangement,the exhaust heat from a cabinet positioned at the windward side must beprevented from being drawn in by the cabinet directly above saidcabinet, that is, the exhaust heat from the windward shelf should not beintroduced into a cabinet positioned at the leeward side. To satisfythis requirement, air inlet 26 is provided at the suction (or draw-in)side, and air outlet 27 is provided at the exhaust side. The air inlet26 and air outlet 27 have a structure in which the wind direction ischanged using partition plate 28. The outside air is introduced from thefront side of the device into the air inlet 26, while the air heated bya heated printed circuit board is expelled from the air outlet 27 to theback side of the device, so that the air in front of the device is drawnin and then expelled. According to this structure, even if a pluralityof cabinets 22 are stacked, each cabinet is not affected by anothershelf.

The air filter 29 whose object is dustproofing has a plate shape, inwhich both the dust collecting efficiency and pressure loss are uniform.The air filter 29 is inserted between the windward side of the fan unit25 and air inlet 26, or in the inlet 26, so as to prevent dust fromentering the cabinet 22 and fan unit 25. Generally, an air filter hasthe characteristic that the higher the speed of the wind passing throughthe filter, the greater the pressure loss is. Therefore, according tothe basic “continuation” principle (i.e., conservation of mass) inhydrodynamics, the portion having a wider cross-sectional area of theair-flow passage has a lower wind velocity, and can be effectively used.

In the air inlet 26 having the structure (see FIG. 8) in which the winddirection can be selected using partition plate 28, the air filter maybe mounted at the entrance of the inlet 26 (i.e., at the most windwardside) in the vertical direction, or at the exit side of the air inlet26, that is, directly below the fan unit 25 in the horizontal direction.In consideration of the above-described characteristics of the airfilter, it is generally preferable and efficient to arrange the airfilter 29 in the horizontal direction, as shown in FIGS. 7 and 8.

In addition, the air filter 29 can be detached or removed from the frontside or face of the device, for maintenance such as the periodiccleaning, replacement, and the like.

Below, the operation of the conventional example will be explained.

When the fan 24 is activated so as to start the forced air coolingoperation, the outside air in front of the device is forcibly introducedfrom the air inlet and passes through the air filter 29, so that dustincluded in the air is removed and the clean air flows into the cabinet22. The air introduced into the cabinet 22 absorbs the heat from eachprinted circuit board 21, and the main portion of the air is expelledfrom the air outlet 27 towards the rear of the device while theremaining portion is expelled through gaps or crevices of the cabinet 22to the outside. Each printed circuit board 21 is cooled by the generatedair flow in the shelf.

As for the wind drawn in by axial fan 24, the spread of the ventilatedarea in the radial direction with respect to the rotational axis canhardly be observed in the vicinity of fan 24, and the cross-sectionalarea of the air flow (when passing through the air filter 29 inserteddirectly below the fan 24) is approximately equal to the projected areaof the fan. That is, the air flow is concentrated within a limited areaof the air filter 29.

In the above-explained dustproof structure employing the forced aircooling method, the air filter 29 is positioned directly below each fan24; thus, the shorter the distance between the air filter 29 and the fan24 is, the stronger the tendency for the air flow to concentrate withina limited area is. Due to such concentration, the dust collectingefficiency and economical efficiency are degraded, the velocity of thewind passing through the air filter 29 becomes higher, and the pressureloss becomes grater.

SUMMARY OF THE INVENTION

In consideration of the above circumstances, an object of the presentinvention is to provide a dustproof structure for a communicationdevice, in which the whole area of the air filter can be effectivelyused, the dust collecting efficiency can be improved at low cost, and anincrease in the pressure loss can be prevented.

Therefore, the present invention provides a dustproof structure of acommunication device, comprising:

a shelf having an air inlet for introducing the air and an air outletfor expelling the air, wherein at least one printed circuit board of thecommunication device is mounted in the shelf;

at least one fan mounted in the shelf; and

an air filter, provided between the fan and the air inlet, forpreventing dust from entering the inside of the shelf, and

wherein the outside air is drawn in by the fan through the air filterinto the shelf so that the printed circuit board is cooled; and

the dust collecting efficiency and the pressure loss of the air filterare not uniform, and have a distribution such that an area of the airfilter closer to the fan, within which the air flow is concentrated, hasa higher dust collecting efficiency, and another area farther from thefan has a lower pressure loss.

The present invention also provides a dustproof structure having asimilar basic structure, but wherein the air filter comprises a firstair filter section and a second air filter section, wherein the firstair filter section is provided at an area closer to the fan, withinwhich the air flow is concentrated, and the second air filter section isprovided at another area farther from the fan, and the first air filtersection has a dust collecting efficiency higher than that of the secondair filter section, while the second air filter section has a pressureloss lower than that of the first air filter section.

Typically, the first and second air filter sections are detachablyinstalled on the shelf.

The present invention also provides a dustproof structure having asimilar basic structure, but wherein in the air filter, a plurality ofair filters are layered in an area closer to the fan, within which theair flow is concentrated.

The present invention also provides a dustproof structure having asimilar basic structure, but wherein in the air filter, the thickness ofan area closer to the fan, within which the air flow is concentrated, isgreater than that of the other area.

In the above two structures, typically, the air filter area closer tothe fan and the other area are detachably installed on the shelf.

The present invention also provides a dustproof structure having asimilar basic structure, but wherein in addition to said air filter,another air filter is provided at the windward or leeward side of anarea closer to the fan, within which the air flow is concentrated.Typically, said air filters are detachably installed on the shelf.

In the above-described structures, typically, the fan is an axial fan.

According to the present invention, the employed air filter has thedistributed dust collecting efficiency and pressure loss in a mannersuch that an area closer to the fan has a higher dust collectingefficiency, while another area farther from the fan has a lower pressureloss of the air flow. Therefore, an expensive air filter having a highdust collecting efficiency is only necessary for an area close to thefan, within which the air flow and dust concentrate, thereby realizing amuch economical dustproof structure.

Also in the air filter, only such an important area within which the airflow and thus the dust concentrate can have a higher pressure loss;thus, the total pressure loss of the air filter can be greatly reducedand the load of the air blowing system of the communication device canalso be reduced.

It is also possible to reduce the pressure loss of an area farther fromthe fan (that is, an area where it is preferable to have a larger airvolume or rate) in comparison with the other area. That is, thedistribution of the pressure loss of the air filter can be controlled,so that the distribution of the air volume in the communication devicecan be controlled.

In addition, the air filter can be detachably installed on the shelf;thus, during maintenance, only the area to which a high concentration ofdust particles have adhered needs to be replaced, thereby improving theeconomical efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the dustproof structure employed ina communication device, in an embodiment of the present invention.

FIG. 2 is a sectional view along line A—A in FIG. 1.

FIG. 3 is a cross-sectional view of the dustproof structure of the aboveembodiment.

FIG. 4 is a cross-sectional view of the air filter of the dustproofstructure in another embodiment of the present invention.

FIG. 5 is a cross-sectional view of the air filter of the dustproofstructure in another further embodiment of the present invention.

FIG. 6 is a cross-sectional view of the air filter of the dustproofstructure in another further embodiment of the present invention.

FIG. 7 is a perspective view of a conventional dustproof structure of acommunication device.

FIG. 8 is a cross-sectional view of the dustproof structure shown inFIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the embodiments of the dustproof structure according to thepresent invention will be explained in detail with reference to thedrawings (FIGS. 1 to 6).

FIG. 1 is a perspective view showing the dustproof structure employed ina communication device, in an embodiment of the present invention, FIG.2 is a sectional view along line A—A in FIG. 1, and FIG. 3 is across-sectional view of the dustproof structure of this embodiment.FIGS. 4 to 6 respectively show cross-sectional views of the air filterof the dustproof structure in another embodiment of the presentinvention.

During the operation of a communication device, electronic components oneach printed circuit board become heated, and this thermal stressdegrades reliability. Therefore, it is necessary to cool the heatedportions by natural or forced air cooling. If forced cooling having ahigher cooling efficiency is used, a large number of dust particlesincluded in the air flow into the communication device together with theair, thereby causing undesirable effects such as contact failure,insulation failure, promotion of corrosion, or the like. An air filteris provided for preventing the dust from flowing into the device.

In FIG. 1, reference numeral 1 indicates an printed circuit board, andreference numeral 2 indicates a cabinet in which a plurality of printedcircuit boards 1 can be mounted. A fan shelf 3 is positioned below theshelf 2, and one or more fans 4 mounted in fan unit 5 is inserted in thefan shelf 3. Each fan 4 is an axial fan and the wind direction thereofcorresponds to the blowing direction. The outside air is drawn in by thefans 4 into the cabinet 2 so as to cool the target area.

The cabinet 2 is not always used in a single structure, but a pluralityof cabinets 2 may be stacked one on the other. In such an arrangement,the exhaust heat from a cabinet positioned at the windward side must beprevented from being drawn in by the cabinet directly above saidcabinet, that is, the exhaust heat from the windward cabinet should notbe introduced into a cabinet positioned at the leeward side. To satisfythis requirement, air inlet 6 is provided at the suction side, and airoutlet 7 is provided at the exhaust side. The air inlet 6 and air outlet7 have a structure in which the wind direction is changed usingpartition plate 8. The outside air is introduced from the front side ofthe device into the air inlet 6, while the air heated by a heatedprinted circuit board is expelled from the air outlet 7 to the back sideof the device.

In order to prevent dust from entering the inside of the shelf 2 and fanunit 5, the air filter 9 used for the dustproof effect is positioned inthe horizontal direction (i) between the windward side of the fan unit 5and the air inlet 6, or (ii) at the most leeward side of the air inlet6, that is, in an area having a wider cross-sectional area of the airflow.

As shown in FIG. 2, the air filter 9 in the present embodiment comprisesframe 10, which is divided into a plurality of sections; air filters 9 a(corresponding to the second air filter section in the presentinvention) and air filters 9 b (corresponding to the first air filtersection in the present invention) respectively and selectively attachedto each section, the air filters 9 a and 9 b having different dustcollecting efficiencies and pressure losses; and cover 11 for preventingthe air filters 9 a and 9 b from dropping out from the frame 10. Thecover 11 is a plate (such as an art metal) with a wide opening area,that is, having the minimum area necessary for preventing each airfilter 9 a or 9 b from falling out.

Each air filter 9 a is a cheap component manufactured regarding pressureloss as more important than dust collecting efficiency, that is, the airfilter 9 a has a lower pressure loss. In contrast, each air filter 9 bis a relatively expensive and high-performance component manufactured inconsideration of the dust collecting efficiency.

The air flow passing through the air filter 9 is not uniform over thewhole area, and has the distribution of air volume (or rate) accordingto the arrangement of fans 4. In particular, the air flow mainlyconcentrates within the area directly below each fan 4. Therefore, thehigh-performance air filters 9 b having a higher dust collectingefficiency are arranged in an area within which the air flow isconcentrated, while the cheaper air filters 9 a having a lower pressureloss are arranged in the remaining area.

In addition, the air filter 9 can be removed and detached from the frontside or face of the device, for maintenance such as the periodiccleaning, replacement, and the like.

Below, the flow of the cooling air flow in the above-explainedembodiment will be explained using FIG. 3.

When the fan 4 is activated so as to start the forced air coolingoperation, the outside air in front of the device is forcibly introducedthrough the air inlet 6 and passes through the air filter 9, so thatdust included in the air is removed and the clean air flows into thecabinet 2. The air introduced into the cabinet 2 absorbs the heat fromeach printed circuit board 1, and the main portion of the air isexpelled from the air outlet 7 towards the rear of the device while theremaining portion is expelled through gaps or crevices of the cabinet 2to the outside. Each printed circuit board 1 is cooled by the generatedair flow in the cabinet.

As for the wind drawn in by each axial fan 4, the spread of theventilated area in the radial direction with respect to the rotationalaxis can hardly be observed in the vicinity of the fan 4, and thus theair flow mainly concentrates within the area directly below each fan 4and accordingly dust also increases there.

In the present embodiment, the air filters 9 b are arranged in suchareas within which the air flow concentrates; thus, dust is concentratedwithin the area of high-performance air filters 9 b having a higher dustcollecting efficiency.

In addition, the air filters 9 a have a lower pressure loss; thus, thewind can pass through these filters 9 a much more smoothly than passingthrough the air filters 9 b having a higher pressure loss. That is, thewind also passes through the air filters 9 a, and as a result, the windpasses through most of the surface of the air filter 9.

In the above-explained embodiment, two kinds of air filters 9 a and 9 bhaving different dust collecting efficiencies and pressure losses areused. However, as shown in FIG. 4, a single kind of air filters 9 a maybe used, and such filters may be layered in an area within which the airflow is concentrated. As another modification of using such an airfilter having a uniform characteristic, the thickness of air filter 9 amay be varied as shown in FIG. 5.

Furthermore, as shown in FIG. 6, a single plate main air filter 9 ahaving a uniform dust collecting efficiency and pressure loss is used,and another detachable air filter 9 a having a smaller area is alsoprovided at the windward or leeward side of an area (of the main airfilter 9 a) within which the air flow is concentrated. According to thisarrangement, similar effects can be obtained.

As explained above, according to the embodiments of the presentinvention, in a communication device having a cabinet 2 in which printedcircuit boards are mounted, the forced air cooling method using fans 4is employed so as to cool the heat generated from each printed circuitboard 1. However, if the forced air cooling method is applied to adevice used in a location full of dust, much of dust included in the airflows into the communication device together with the air. In order toprevent such an inflow of dust, air filter 9 is provided at the windwardside of fans 4.

When the fan 4 is activated and the forced air cooling operationcommences, the air is forcibly introduced into air inlet 6 and passesthrough the air filter 9, so that the filtered air without dust is drawninto the cabinet 2. This air introduced into cabinet 2 removes heat fromeach printed circuit board 1, and then is expelled through air outlet 7to the outside of cabinet 2. The printed circuit board 1 is cooled bythis air flow caused by the above operation.

Here, if the distance between each fan 4 and air filter 9 is short, theair flow passing through the air filter 9 is concentrated within alimited area directly below the fan 4. However, in the presentembodiment, the air filter 9 is divided into a plurality of sections;thus, a high-performance air filter having a high dust collectingefficiency can be provided only at an area within which the air flow andthus the dust are concentrated. In addition, only an air filter orfilters to which a high concentration of dust clings need to bereplaced.

That is, the air filter 9 is divided into a plurality of sections, anddifferent kinds of air filters are selectively used for an area withinwhich the air flow is concentrated and for another area without suchconcentration, thereby realizing a much more economical dustproofstructure having a higher dust collecting efficiency.

What is claimed is:
 1. A dustproof structure of a communication device,comprising: a cabinet having an air inlet for introducing the air and anair outlet for expelling the air, wherein at least one printed circuitboard of the communication device is mounted in the cabinet; at leastone fan mounted in the cabinet; and an air filter, provided between thefan and the air inlet, for preventing dust from entering the inside ofthe cabinet, and wherein the outside air is drawn in by the fan throughthe air filter into the cabinet so that the printed circuit board iscooled; and in addition to said air filter, another air filter isprovided at the windward or leeward side of an area closer to the fan,within which the air flow is concentrated.
 2. A dustproof structure asclaimed in claim 1, wherein said air filters are detachably installed onthe cabinet.
 3. A dustproof structure as claimed in claim 1, wherein thefan is an axial fan.